The novel polyesters of the present invention comprise copolymers made from rigid (made from a self-condensing hydroxy acid moiety) ester units of an alkylene oxybenzoate and one of the following flexible (made from a diacid moiety and a diol) ester sequences: (1) an alkylene 2-alkenyl- (or alkyl-) succinate; or (2) an alkylene dimerate (from the dimer of a long chain unsaturated fatty acid).
Two p-(hydroxyalkoxy)benzoic acids; p-(hydroxybutoxy)benzoic acid and p-(hydroxypropoxy)benzoic acid, have been used in the production of modified poly(trimethylene terephthalate) fibers and films with improved strength and dimensional stability with no mention of a change in flexibility [Jap. Pat. Appl. No. 20474/69; Chem. Abstracts 72, 4277e (1970)]. The p-(hydroxypropoxy)benzoic acid was also used to modify poly(ethylene terephthalate) to study isomorphism in the system [J. Polym. Sci. A-2, 4361 (1964)].
The prior art does not disclose the use of AB type (i.e., self-condensing) polyesters as the precursor of crystalline hard sequences, or combining the AB oxybenzoate moieties with sequences bearing flexible chain components to produce the unique flexible copolyesters of this invention.
The homopolymer of p-(hydroxyethoxy)benzoic acid has been converted into fibers which exhibit lower crystallinity and tensile strength when compared to PET. The fibers of the homopolymer exhibit a high modulus and rigidity compared to other known monofilament sutures and seemingly preclude the use of the ethylene oxybenzoate moieties in copolymers used to produce strong but flexible fibers. [Angew. Makromol. Chem. 40/41, 41 (1974)].
U.S. Pat. Nos. 3,542,737; 3,651,014; 3,682,863; 3,890,279; and 4,388,926, as well as Angew, Makromol. Chem. 58/59, 229 (1977), disclose the use of polyether, dimerate, and 2-alkenyl succinate in the production of thermoplastic copolyester elastomers, but do not disclose their use with an AB type polyester such as the poly(alkylene oxybenzoates) of the present invention, nor do they suggest that the copolyesters of the present invention could produce the unexpectedly strong but compliant monofilaments of the present invention.
Monofilament sutures are preferred by surgeons for many surgical applications due to their inherent smoothness and noncapillarity to body fluids. Most synthetic monofilament sutures are relatively stiff. Besides making the material more difficult to handle and use, suture stiffness or low compliance can adversely affect knot tying ability and knot security.
In addition, high compliance under low stress allows the suture or other wound closure or approximation device to yield as a wound swells, so that the suture or device do not place the wound tissue under tension, which might cause tearing, cutting, or necrosis of the tissue.
The problems associated with the use of low compliance sutures in certain applications were recognized in U.S. Pat. No. 3,454,011, where it was proposed to fabricate a surgical suture composed of Spandex polyurethane. Such sutures, however, were too elastic and did not find general acceptance by the medical profession.
Recently issued U.S. Pat. No. 4,224,946 describes a monofilament suture with good flexibility and knot strength, which suture is composed of block polyetheresters which contain (1) a polymeric block of polyalkene ethers and (2) a polymeric block of aromatic dicarboxylic acids or cycloaliphatic acids with short chain aliphatic or cycloaliphatic diols. In addition, application Ser. No. 218,998 (now U.S. Pat. No. 4,388,926) discloses high compliance monofilament sutures of poly(tetramethylene terephthalate-CO-(2-alkenyl or alkyl)succinate.
It is an object of this invention to provide novel flexible polyesters which can be melt processed at moderately low temperatures to produce useful surgical sutures and allied surgical products and more particularly strong but compliant monofilament sutures having unique handling and knot tying characteristics.